Formation of hydrogen molecules on interstellar grain surfaces

The problem of the formation of hydrogen molecules from hydrogen atoms in interstellar dust clouds is reconsidered, and the physical bases of relations between (a) the heats of adsorption of hydrogen atoms on dust grains and (b) the grain surface temperatures are reviewed and reexamined. To be specific, the case of graphite grains is considered throughout. The analysis differs from previous work at several points, and some of the conclusions are accordingly different.